The primary intent is to determine principles governing the prevention or alleviation of forgetting in the developing rat, with special reference to learning that takes place during infancy. Specific experiments would test rats in the age range of about 6 days postnatal to adulthood, in terms of a variety of recently developed operant and classical conditioning tasks. Separate sets of studies are directed toward tests of two general hypotheses concerning "infantile amnesia" (the exaggerated forgetting seen following a relatively long retention interval, for infants relative to older animals). One set tests the hypothesis, shared by several theories, that infantile amnesia is due to age-specific characteristics of original learning. These tests will assess stimulus selection by rats in their infancy and older, applied in conjunction with certain environmental variables that seem of special importance for infantile behavior. Specific experiments will test, ontogenetically, phenomena such as blocking, overshadowing, stimulus-reinforcer interactions, and the influence of redundant contextual stimuli. Special attention will be given the consequences of such behavior for later retention and to rats younger than the age of weaning (21 days). Effects of the home environment, ambient temperature, and time during the light-dark cycle at which testing is conducted, will be tested in terms of their influence on stimulus selection, learning and retention. The second set of studies tests an equally widespread hypothesis, that infantile amnesia is unique among sources of forgetting in its resistance to prevention or alleviation in the absence of drastic physiological intervention. These tests assess the relative susceptibility of infant rats to relatively innocuous conditions that lead to alleviation or prevention (relatively speaking) of forgetting among adults. Specific experiments will test, for infants and adults, the influence of prior cueing on retention, multiple vs. single prior cueing treatments and the relative characteristics of a memory made active by a prior cueing treatment, ontogenetic changes in the reduction in forgetting that accompanies widely distributed acquisition trials or high degrees of training, and the relationship between processes that accompany distributed conditioning trials and those that accompany prior cueing treatments.